1. Field of the Invention
The present invention relates to a process for the preparation of 4,4'-dihydroxybiphenyl.
2. Discussion of the Background
4,4'-Dihydroxybiphenyl is useful, for example, for the production of liquid crystalline polyesters.
A number of procedures for the preparation of 4,4'-dihydroxybiphenyl are known. One method consists of first sulfonating biphenyl and then saponifying it. This process is not only expensive but also involves substantial disposal problems. Therefore, preparation from 3,3',5,5'-tetra-t-butyldiphenoquinone is preferred. For example, U.S. Pat. No. 3,631,208 describes a process for the preparation of 4,4'-dihydroxybiphenyl by the reduction of tetra-t-butyldiphenoquinone with 2,6-di-t-butylphenol in the presence of an amine, followed by dealkylation in the presence of an aluminum phenolate at temperatures of approximately 280.degree. C. The intermediate 3,3',5,5'-tetra-t-butyl-4,4'-dihydroxybiphenyl is precipitated with a suitable precipitant and optionally recrystallized. A variation of this process is described in Russian Patent No. 1,011,626, in which the dealkylation is carried out in decalin, undecane, or tridecane in the presence of a trialkylphenolate.
U.S. Pat. No. 4,482,755 discloses the reduction of 3,3',5,5'-tetra-t-butyldiphenoquinone using a heterogeneous catalyst (for example, Pd/C). After separation, the product is dealkylated using an acidic ion exchanger. A drawback of this procedure is the formation of substantial amounts of by-products. The acid-catalyzed dealkylation can also be carried out with sulfuric acid (Japanese Patent Application No. 83/189,127 and U.S. Pat. No. 4,354,047) or p-toluenesulfonic acid in a suitable solvent (Japanese Patent Application No. 85/23,338 and U.S. Pat. No. 4,354,048).
Thus, according to the previously known processes, it is necessary to carry out the reaction in a solvent and to isolate the 3,3',5,5'-tetra-t-butyl-4,4'-dihydroxybiphenyl formed as an intermediate. Both steps are costly and hinder the availability of the target product.